This invention relates to a built-up wheel suitably used for vehicles, especially, two-wheel vehicles.
Various types of built-up wheels for vehicles have heretofore been proposed, each of which consists of parts of different materials, which are combined together unitarily by fastening means, such as bolts, so as to reduce the weight of the wheel. These built-up wheels include, for example, a built-up wheel disclosed in Japanese Utility Model Laid-open No. 36077/1980 which is made by fastening a rim of synthetic resin and a metallic wheel disc to each other unitarily in their radial direction by bolts, and a built-up wheel disclosed in Japanese Utility Model Publication No. 26805/1983 and made by engaging a rim of synthetic resin and a metallic wheel disc with each other in their axial direction and fastening the engaged portions to each other unitarily by bolts. Although these built-up wheels have a smaller weight, stress tends to be concentrated in the fastened portions of the rim and wheel disc. This poses problems in the strength and durability of the built-up wheels so that such built-up wheels are substantially not suitable to be put to practical use.
Moreover, in the above-mentioned built-up wheels, mud and soil are deposited on the portions thereof which are fastened together by bolts. It is troublesome to clean such soiled portions, and such deposit on the wheels spoil the external appearance thereof. Namely, these built-up wheels have various kinds of faults.
There is a known built-up wheel in which a main portion except the tire is formed of synthetic resin. Such a built-up wheel of synthetic resin is inferior in the strength and rigidity to a metallic built-up wheel. If a wheel as a whole is formed of a recently-developed fiber-reinforced synthetic resin of a high modulus of tensile elasticity (3000-70000 kg/mm.sup.2), such as a carbon fiber-reinforced resin so as to eliminate these faults of the wheel of synthetic resin, the reduction of the manufacturing cost and weight thereof, which is a basic object of the production of built-up wheels of synthetic resin, cannot be attained since the above-mentioned reinforced resin has an extremely high price and a high specific gravity (1.74-1.84).